a feedback system is a rating system smilar to ebay's feedback system.
it will let you rate a user, you may give a user a negative or positive feedback.
the feedback system will let you post your feedback, only after you completed a purchase.
the feedback system will help buyers decide if he will purchase from that user, based from his feedback.
of course if it were me, i will be hesitant to buy from a seller who has a lot of negative feedbacks.
negative feedbacks means, buyers that bought from the user had a lots of compalints and dis-satifsfaction.
while, giving a positive feedack to a seller means, a buyer is very much satisfied with the service and products of the seller.